Installed pipelines in buildings and underground can be rehabilitated without opening structures or digging the ground. The trenchless rehabilitation enables a quick and durable rehabilitation of pipes within buildings and underground pipelines. A resin impregnated liner is installed in a pipe with an inversion drum by using air pressure to invert the liner into the pipe. Typically, a plastic-coated polyester felt tube, i.e. the liner, is first impregnated with a synthetic resin. The impregnated liner is closed at one end and wound up inside a lining drum around a shaft. The open end of the liner is fastened around an outlet of the lining drum. When pressurized air is supplied to the lining drum, the liner, due to the influence of air pressure, starts to protrude inside the lining drum, and the protruding liner is directed into the pipe to be renovated by unwinding the liner from the shaft by rotating the shaft so that the liner starts to extend through the outlet of the lining drum.
Once the liner is installed, air pressure is maintained on an elevated level until the resin within the liner settles and the liner forms a rigid pipe against the inner surface of the old pipe. The lining drums of the prior art have been welded together from several metal parts. The liners can typically withstand pressures from 80 kPa to 200 kPa inside the liner without rupture when the liner is in an open space. In a confined space, the liner does not have space to expand or rupture. Therefore, the pressure can rise much higher than the above pressure interval. For these scenarios, the lining drums have been equipped with a safety valve which opens when the air pressure inside the lining drum reaches 100-300 kPa, depending on the lining drum. Typical output from an air compressor that feeds the lining drum is in a range of 800-1000 kPa. Usually a pressure regulator is used between the air compressor and the lining drum as a third safety feature in addition to the safety valve in the liner itself.
One problem associated with the above prior art arrangement is that even the three independent safety features do not prevent explosions of the lining drum due to the excessive pressure that builds up inside the lining drum. A liner that is tangled inside the lining drum can block both the outlet and the safety valve. An explosion of the lining drum is a potentially a lethal accident and must be avoided at all cost.
One object of the present invention is to provide a low-pressure lining drum that is safer to use than the lining drums of the prior art because the structure of the lining drum does not allow an excessively or dangerously high pressure to build up inside the lining drum.
One advantage of the arrangement of the present invention is that the device is safe to use due to the pressure relief arrangement that cannot be blocked by the liner from the inside of the device.